One other thought (funny how you always get that after you press the send button).
If you did have your children tested, and 1 came back positive, how would that make you feel and would you treat that 1 differently. Maybe that 1 would get better birthday presents than their siblings, or maybe you wouldn't want them to do "tough" stuff like their siblings. You could alienate the healthy children from their "might get sick" sibling. Love them all equally and allow them to be kids.
In the end it's your decision, but it's hard to close Pandora's box once it's opened.